1. Field of the Invention
The present invention relates to a shock-absorbing steering column apparatus which has a structure capable of absorbing the shock of collision in a cylindrical steering column passing through a steering shaft supported for example on a lower face of the dash board of an automobile and constituting the steering apparatus thereof, thereby protecting the life of the passenger at the collision.
2. Related Background Art
At the collision of automobiles, so-called primary collision between the automobiles is often followed by so-called secondary collision in which the driver collides with the steering wheel.
In order to reduce the impact to the driver at such secondary collision and to protect the life of the driver, there has already been employed, as the steering shaft supporting the steering wheel at an end thereof, so called collapsible steering shaft of which the entire length is reducible under the application of a strong impact, and a shock-absorbing structure in the steering column through which the steering shaft passes.
A shock-absorbing steering column used for such purpose is already disclosed for example in the Japanese Laid-Open Utility Model Sho 63--6578.
Such conventional shock-absorbing steering column apparatus are constructed as shown in FIGS. 9 to 12.
Referring to FIG. 9, a steering shaft 1 has a steering wheel 2 at the upper end thereof and is rotated by said steering wheel 2. Said steering shaft 1 has a collapsible structure (not shown) which, upon receiving an axial impact, reduces the entire length while absorbing said impact.
A tubular steering column 3, housing said steering shaft 1 therein, is supported at the middle and at the lower end by a part of the frame 4 of the automobile, such as the lower face of the dash board. More specifically, the lower end of the steering column 3 is axially slidably supported by a bracket 5 fixed in a part of the frame of the automobile.
On the other hand, on the external periphery in the middle of the steering column there is fixed, for example by welding, an upper bracket 6 formed by folding a metal plate. On both sides of said upper bracket 6 there are formed mounting plates 7, for mounting said bracket 6 onto the body 4, having U-shaped notches 8 opening at lateral edges of the mounting plates 7 facing the steering wheel 2.
A fixing member 9, made for example of a plastic material and formed in a square U-shape, is fitted on a lateral edge of said mounting plate 7, so as to cover said notch 8, and a bolt 10 inserted through a hole 25 formed on said fixing member 9 and said notch 8 is screwed into a threaded hole formed in the body 4, whereby said fixing member 9 pinches the mounting plate 7 and fixes said upper bracket 6 to the body of the automobile.
An energy absorbing member 11 is welded, at an end thereof, to the mounting plate 7, and is provided, at the other end, with a hole 26, in which said bolt 10 is inserted. Said energy absorbing member 11, made of a strip-shaped material capable of plastic deformation, is provided, in the middle thereof, with a U-shaped folded portion 12, which is pinched between said mounting plate 7 and a guide plate 13 to be explained in the following.
The guide plate 13, formed by pressing a metal plate, is welded to the lower part of the mounting plates 7 at each side of the upper bracket 6, thereby defining a guide space 14, between the upper face of each guide member 13 and the lower face of each mounting plate 7, for accommodating said folded portion 12 of the energy absorbing member 11.
The shock-absorbing steering column explained above functions in the following manner for protecting the life of the driver, at a collision of the automobile.
An impact applied to the steering wheel resulting from the secondary collision in an accident is immediately transmitted to the steering column 3, thus strongly pushing the steering column 3 in the axial direction thereof.
When the axial impact applied to the steering column 3 exceeds the friction between said mounting plates 7 and the fixing members 9, the bolts 10 are disengaged from the notches 8 formed in said mounting plates 7, whereby the steering column 3 becomes capable of displacement.
As a result, the steering column 3 moves axially to the front (towards lower left in FIG. 9) by said impact, thus stretching the energy absorbing member 11 as shown in FIG. 12. In the course of stretching of said member 11 from a state shown in FIG. 9 to a state in FIG. 12, the folded portion 12 formed in the middle of said member 11 moves from an end connected to the bolt 10 to the other end connected to the mounting plate 7 (from right to left in FIG. 12).
In said movement, each portion of the energy-absorbing member 11 performs plastic deformation, absorbing the impact applied from the body of the driver to the steering column 3 through the steering wheel 2. In the illustrated example, a part of the upper face of the guide member 13 is inclined, in such a manner that the height of the guide space 14 accommodating the folded portion 12 of the energy-absorbing member 11 gradually decreases, whereby said member 11 absorbs progressively increasing impact and achieves effective impact absorption.
However, the above-explained conventional shock-absorbing steering column inevitably requires complex assembling operations, because of the large number of component parts involved.
More specifically, in the above-explained conventional structure, ends of the energy-absorbing members 11 are welded to the mounting plates 7 of the upper bracket 6, and the guide plates 13 are also welded to said upper bracket 6. Such separate welding operations of different parts to the upper bracket 6 complicate the administration of parts and the assembling operations, thereby inevitably increasing the manufacturing cost of the shock-absorbing steering column.